2003 4x4 AC LSD Swap

Hi all, I’ve got a 2003 4x4 V8 AC with an open 3.90 gear ratio open rear differential. The pinion bearing on it has gone out so I’m looking to replace the whole thing and am considering putting in a 3.90 LSD. Is there anything to watch out for or are they interchangeable?
Thanks!

 

Interchangeable.

Just use motul 90pa, lucas 80w-90 or NON synthetic fluid with friction modifier.

 

Literally the only synthetic fluid that seems to work with the factory LSD is from Valvoline, and Amsoil Severe Gear. I thought I knew better and went with my preferred oil, Mobil1 LS, got chatter. Had to dump like $80 in fluid out. Replaced with Lucas 80w90 dino gear oil. No issue.

This and other topics covered in the community 1st gen info megathread.

 

Beware if you use one from an '05 or '06 that the companion flange is different (larger), and you'll have to either change it (and set the preload, which entails more parts and skill and $...it cost me ~ $450 to rework my $400 used 3rd.), or change the slip yoke to match (again, more $). Since you're 2WD you can use either the 3.909 (11 x 43) or 3.90 (10 x 39) gears. I chose to use the OEM paper gasket, but others just use RTV.

Many will recommend getting an Eaton locker from East Coast Gear Supply ($$$), since it's possible that a used LSD will have mostly worn clutch plates anyway. In hindsight, I should have done this.

 

Thanks guys,
It is a 4x4, I'm looking at an LSD that is listed as a 3.90 gear ratio. The listing says it's from a Sequoia, but the description says it's from an '04 Tundra (trying to confirm which is true); but anyway, is there knowledge of if a 3.90 will be a problem or does it come down to a rounding error?

 

It's funny how the same threads seem to pop up all of the time
Third member replacement | Toyota Tundra Forum
Mismatched diffs…. | Toyota Tundra Forum
2005 4x4 regear questions | Toyota Tundra Forum
Rear diff | Toyota Tundra Forum

Anyway, here is some fun info

2000-2003
3.91 - V8, 4x4, auto trans
3.92 - V8, 4x2, auto trans
4.08 - V6, 4x2, auto trans or manual trans
4.10 - V6, 4x4, manual trans
4.30 - V6, 4x4, auto trans

2004, Regular Cab or Access Cab
3.91 - V8, 4x4, auto trans
3.92 - V8, 4x2, auto trans
4.08 - V6, 4x2, auto trans or manual trans
4.10 - V6, 4x4, manual trans
4.30 - V6, 4x4, auto trans

2004, Double Cab
4.08 - V8, 4x2, auto trans
4.10 - V8, 4x4, auto trans

2005-2006
3.77 - V6, 4x2, auto trans
3.91 - V8, 4x4, auto trans
3.92 - V8, 4x2, auto trans
4.08 - V6, 4x2, manual trans

 

Thanks for the info! Just trying to make sure I don't blow anything up with a difference in ratios, but 3.90 and 3.909 are very close regardless.
I know on the one I'm looking at I'll have to swap the pinion flange, but I'm confident I can handle that.

 

You mean you don't want to do what a shady mechanic seller did to this member?

Sad I can remember that one. I'd have been tempted to shank that seller in the neck. And my mechanic who supposedly looked it over. @Burgmane is a better human than I am

 

3.91 actually equals 3.909091 (43/11)
I know...picky, picky, picky!

It only matters if you have to match the front gears

 

Well, I do have to match which is why I was making sure haha